A prior-art vehicle door lock device is disclosed in Patent Document 1. This vehicle door lock device includes a mounting member, a fork, a pawl and a switching lever.
The mounting member is provided on a door that opens and closes in a vehicle width direction relative to a vehicle body. A striker is fixed to the vehicle body; the mounting member is formed with an entry opening, into which the striker is inserted. A fork is pivotably provided on the mounting member. The fork is switchable between a locking state, in which the striker is locked within the entry opening, and a released state, in which locking of the striker within the entry opening is released. The pawl is pivotably provided on the mounting member. The pawl is capable of fixing or allowing pivoting movement of the fork.
The switching lever presses the pawl to switch the fork from the locking state to the released state. More specifically, the switching lever is supported by the mounting member in such a way as to be movable downward by a door opening operation. One end of each of two coil springs, which face each other, is fixed to the right and left sides, respectively, of the switching lever, and the other end of each coil spring is fixed to the mounting member. An engagement protrusion portion, which protrudes downward, and an engagement hole, which surrounds the engagement protrusion portion in a U shape from below, are formed at the center of the switching lever. In other words, the engagement hole is formed by positioning engagement recess portions on the right and left sides of the engagement protrusion portion to define the U-shape by the two engagement recess portions. The pawl includes a ratchet abutting the fork, a rotation shaft having one of its ends integrally coupled to the ratchet, and an opening lever that is integrally coupled to the other end side of the rotation shaft and is formed with an engagement claw portion. The engagement claw portion of the opening lever is inserted into the engagement hole of the switch lever. Therefore, if the switching lever moves downward while the engagement claw portion is positioned under the engagement protrusion portion, the engagement claw portion will come into contact with the engagement protrusion portion.
In the vehicle door lock device having the above-described structure, the switching lever is, in the normal state, in its initial position when the switching lever is substantially perpendicular to the vehicle width direction. In this state, if the switching lever moves downward due to a door opening operation, the engagement protrusion portion of the switching lever presses the engagement claw portion of the opening lever. As a result, the pawl pivots about the rotation shaft, the ratchet moves away from the fork, and the fork is thereby switched from the locking state to the released state.
Furthermore, in this vehicle door lock device, if the door or the vehicle body experiences an impact from the outside of the vehicle due to a side collision or the like, an inertial force will act on the switching lever with respect to the direction of the impact. In this case, the switching lever will compress one of the coil springs and expand the other coil spring to pivot towards the opposite direction of the direction of the impact. As a result, the switching lever will change from a state, in which the engagement protrusion portion is positioned above the engagement claw portion, to a state, in which the engagement claw portion is positioned in the engagement recess portions. In this state, even if a door opening operation is caused by the impact and the switching lever moves downward, the engagement claw portion will not come into contact with the engagement protrusion portion, but instead will be merely displaced within the engagement recess portions. In other words, even if the switching lever moves downward unintentionally, what results is a so-called “swing-and-miss state” in which the engagement claw portion is not pressed, i.e. the fork is not switched from the locking state to the released state. In this way, the prior-art vehicle door lock device prevents an unintended opening of the door at the time of the impact to thereby ensure the safety of the occupants. A similar vehicle door lock device is disclosed in Patent Document 2.